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1. Field of the Invention
This invention relates to a method of excavating a layer of soil by using an excavator comprising a grab with two bucket halves.
2. General Background of the Invention
Excavating methods using a grab are very well-known for excavating soil layers on land or under water.
Soil layers may have to be excavated for various reasons. One reason is that the depth of a water course must be increased. Another, more recent reason is that the soil layer contains contaminated material. In that case care has to be taken that the material of the soil layer is disturbed to a minimal extent, in order to prevent diffusion of the contaminated material into the surrounding water. Usually, contaminated soil layers are relatively thin layers.
In addition, which is true for both land and under-water operation, the amount of removed material must be kept as small as possible.
Furthermore, the excavating process should be as efficient as possible, in order to ensure that the capacity of each excavating cycle is optimal and the required number of movements is kept to a minimum.
Thus, there is a need for an excavating method by which contaminated soil layers can be excavated in a controlled manner.
In addition, there is a need for an efficient excavating method.
Moreover, there is a need for an accurate excavating method for excavating layers of soil material, in particular thin layers of (contaminated or not) material.
Incorporated herein by reference are European Patent No. 067747, its published patent application no. 95200709.4, published on 18 Oct. 1995, and Dutch patent application no. NL 9500450, filed 22 Mar 1994.
According to one aspect, the invention provides a method of excavating a surface layer of soil by using an excavator comprising a grab having two bucket halves with cutting edges, comprising the steps of:
a) in a first excavating position the grab is held in a first orientation as seen in projection on a horizontal plane and inserted into the layer of soil in an open position of the bucket halves until their cutting edges reach a first predetermined level while maintaining said first orientation,
b) while maintaining that level and first orientation, the bucket halves are moved to a closed position during which movement their cutting edges move towards each other through a substantially straight path so as to excavate a first rectangular portion of the layer of soil,
c) the grab is lifted and moved to a discharge position horizontally spaced from the excavating position and emptied there to make further transport of the excavated soil possible,
d) the grab is moved towards a second excavating position and held in said first orientation and inserted into the layer of soil in an open position of the bucket halves until their cutting edges reach a second predetermined level,
e) while maintaining that level and said first orientation, the bucket halves are moved to a closed position during which movement their cutting edges move towards each other through a substantially straight path so as to excavate a second rectangular portion of the layer of soil, said second portion being adjoining to said first portion before excavation,
f) the grab is lifted and moved to a discharge position horizontally spaced from the first and second excavating positions and emptied there to make further transport of the excavated soil possible;
whereafter steps d, e and f are repeated in a corresponding manner for excavating subsequent third, fourth, etcetera rectangular portions until the layer of soil is excavated.
Thus it is ensured that a repeated excavating movement on the same spot is avoided to a large extent and any possible overlap can be known and can be kept as small as possible. The grab can be filled with a portion of the layer of soil, the location and orientation of which is known and thus filled to an optimal capacity. The straight closing movement of the cutting edges and the stable holding of the grab during closing and excavating, minimize the risk of spreading soil particles.
Preferably, the excavation is carried out according to a pattern comprised of adjoining, parallel rectangular portions of the layer of soil, wherein said first and second predetermined levels are on a same level or horizontal plane. In this way a horizontal layer or part of such a layer can be removed by moving the grab one pattern step after each excavating cycle.
In an advantageous further development according to the invention, the excavation is carried out according to a pattern comprised of superposed, in projection in a horizontal plane, coinciding rectangular portions of the layer of soil, wherein said first and second levels are different. In this way a vertical column of two or more excavating portions can be removed.
The cutting edges may be moved through a substantially horizontal path during the closing of the bucket halves, so that a horizontal cutting surface is left after an excavating cycle, which permits a reliable estimate of the actual bottom level and of the quantity of soil which is yet to be excavated.
According to a further development, the angle of the grab with respect to the vertical is measured during insertion of the grab into the layer of soil by means of an inclinometer.
In yet a further development of the method according to the invention, a projection of the area to be excavated is entered into a control and monitoring system for the excavating device in the form of a horizontal template of rectangles corresponding to the rectangular portions to be removed by the grab in an excavating step and determining the location of the grab required for each subsequent excavating step. The prosecution of the excavating process can thus be controlled in a positive and therefore reliable manner.
The orientation of said horizontal template may be selected depending on main profiles in the original surface of the layer of soil, such as a bank of a river or canal, or a harbour.
Advantageously, the rectangles are selected to have a length and a width slightly smaller than the span and the width of the grab, so as to enable a slight and known overlap of the area enclosed by the grab and the rectangles of the horizontal template.
In a further development according to the invention the original location and course of the surface of the layer of soil as well as of the desired location and course of the surface to be obtained by excavation of the layer of soil, are entered into said control and monitoring system for the excavating device in respective digital terrain modelsxe2x80x94such models are known per se in the artxe2x80x94and combined with said horizontal template, the control and monitoring system dividing the area to be excavated into equidistant or parallel and adjacent subareas, each rectangle of the template comprising a plurality of such subareas, and attributing a thickness value to each subarea, said thickness value corresponding to the difference in the levels of the actual surface and the desired surface for that subarea.
Preferably, the control and monitoring system matches a vertical template on the area between the original surface and the desired surface, the vertical template having horizontal grid lines.
According to a further development of the process of the invention the distance between the horizontal grid lines of the vertical template is selected in relation to the volume of the grab divided by the footprint of the grab. The footprint of the grab is the largest surface area of the grab for excavating purposes.
According to a further development of the process of the invention, the control and monitoring system updates the actual level of the surface layer after each excavating cycle by adjusting the level and thickness values for the subareas located in the rectangle concerned in the horizontal template.
According to a further development of the process of the invention, the control and monitoring system shows the actual status of the excavation process for each of the subareas of the rectangles of the horizontal template on a monitor screen. Thus, the operator of the excavator is provided with information about where the grab still has to be moved to and how many times and thus regarding the process of work on a real-time basis.
According to a further development of the process of the invention, the control and monitoring system shows the thickness values in each subarea in hatching, wherein the hatching is a function of the thickness of the layer still to be removed.
In a preferred method according to the invention, the actual position in the world of the grab is determined by a positioning system using local or global coordinate systems, the control and monitoring system being provided with a receiver for use in said positioning system. Preferably, the monitoring of the actual position in the world of the grab is carried out with the aid of a Real Time Kinematic GPS.
According to a further development of the process of the invention, the actual position in the world of a reference point for the excavator is monitored by the control and monitoring system and the position of a grab reference point with respect to the excavator reference point is measured and supplied to the monitor and control system. Advantageously, the grab reference point is selected at the center of the meeting line of the bucket-half edges in closed position. This point is also the centre of the excavating opening of the grab.
According to a further development, the control and monitoring system provides the operator information concerning the position of the rectangle of the horizontal template to which the grab is moved, in particular compares the location of the grab contour or footprint established on the basis of the measured location of the grab reference point with the location of that rectangle and displays the result of that comparison on a monitor screen.
The excavating process is further improved in controllability and accuracy when according to the invention the orientation of the grab in the horizontal and vertical plane is measured and supplied to the monitoring and control system for comparison to the grid orientation. In case the grab is suspended from an arm and boom of the excavator, the orientation of the arm/boom, in the vertical plane relative to a vertical line through the excavator reference point, can be measured and supplied to the monitoring and control system for determining the position of the grab reference point in that vertical plane. Likewise, the orientation of the arm/boom in the horizontal plane relative to the excavator reference point may be measured and supplied to the monitoring and control system for determining the position of the grab in that horizontal plane.
According to a further aspect of the invention, a rotor is used in the connection between the arm/boom of the excavator and the grab and the angle between the grab, in particular a line in a plane of symmetry of the grab, and the arm/boom, considered in a horizontal plane, is measured and supplied to the monitoring and control system for determining the orientation of the grab contour in the horizontal plane.
In one further development of the method according to the invention the excavator is supported on a base plane and the vertical distance from the excavator reference point to the base is entered into the monitoring and control system. Preferably, the orientation of the base plane is measured and the measurements are supplied to the monitoring and control system.
As suggested in the introduction, the excavating may be carried out in a marine environment. This may be done with the excavator positioned on the bank or the shore, the grab arm/boom extending until below the water. Alternatively, the excavator may be positioned on a floating support, such as a barge or a vessel. In that case it is preferred that the soil layer is located below water level.
Rotation of the support about the support reference point in a horizontal plane is measured by a gyro compass, with its measurements supplied to the monitoring and control system for determining the displacement of the grab due to the support rotation.
In case the receiver for the positioning system is located at a distance from the excavator reference point, the location of the excavator reference point relative to the receiver is measured and entered into the control and monitoring system.
The orientation of the base plane in a vertical plane is preferably measured by means of roll and pitch sensors and entered into the control and monitoring system.
From another aspect, the invention provides a method of excavating a surface layer of soil by a using an excavator comprising a grab having two bucket halves with cutting edges, comprising the steps of:
a) matching a horizontal template of parallel and congruent rectangles on the layer to be excavated, each rectangle having a centre;
b) keeping the grab in open position defining a rectangular grab excavating opening having a grab centre;
c) vertically matching the centre of a selected first rectangle and the grab centre and keeping the grab opening in a first orientation parallel to the rectangles of the horizontal template;
d) positively lowering the cutting edges of the bucket halves into the layer of soil until their cutting edges reach a first predetermined level which maintaining said orientation,
e) while maintaining that first level and first orientation, moving the bucket halves to a closed position during which movement their cutting edges move towards each other through a substantially straight path so as to excavate a first rectangular portion of the layer of soil,
f) lifting the grab and moving the grab to a discharge position horizontally spaced from the excavating position and emptied there to make further transport of the excavated soil possible,
g) moving the grab towards a selected second rectangle of said horizontal template and keeping the grab in open position,
h) vertically matching the centre of said second rectangle and the grab centre and keeping the grab opening in said first orientation;
i) keeping the grab in said first orientation and lowering it into the layer of soil in an open position of the bucket halves until their cutting edges reach a second predetermined level,
j) while maintaining that second level and said first orientation, moving the bucket halves to a closed position during which movement their cutting edges move towards each other through a substantially straight path so as to excavate a second rectangular portion of the layer of soil,
k) lifting the grab and moving it to a discharge position horizontally spaced from the first and second rectangles and emptied there to make further transport of the excavated soil possible;
l) repeating step g-k in a corresponding manner for excavating subsequent rectangles of said horizontal template until the layer of soil is excavated.
According to a further development of the process of the invention, said first and second rectangles are horizontally spaced, in particular adjacent to each other.
Alternatively, said first and second rectangles are superposed.
According to a further development of the process of the invention, the rectangles are selected to have a length and a width slightly smaller than the footprint of the grab, so as to permit a slight and known overlap of the area enclosed by the grab and the rectangles of the horizontal template to ensure complete enclosure of the sediment to be removed.
According to a further development of the process of the invention, the original location and course of the surface of the layer of soil as well as of the desired location and course of the surface to be obtained by excavation of the layer of soil are entered into a control and monitoring system for the excavating device in respective digital terrain models and combined with said horizontal template, the control and monitoring system dividing the area to be excavated into equidistant or parallel and adjacent subareas, each rectangle of the template comprising a plurality of such subareas, and attributing a thickness value to each subarea, said thickness value corresponding to the difference in the levels of the actual surface of the desired surface for that subarea.
According to a further development of the process of the invention, the control and monitoring system matches a vertical template on the area between the original surface and the desired surface, the vertical template having horizontal grid lines.
According to a further development of the process of the invention, the distance between the horizontal grid lines of the vertical template are selected in relation to the volume of the grab divided by the span area of the grab.
According to a further development of the process of the invention, the control and monitoring system updates the actual position of the surface layer after each excavating cycle by adjusting the thickness values for the subareas located in the rectangle concerned in the horizontal template.
According to a further development of the process of the invention, the control and monitoring system shows the actual status of the excavation process for each of the subareas of the rectangles of the horizontal template on a monitor screen.
According to a further development of the process of the invention, the control and monitoring system shows the thickness values in each subarea in hatching, wherein the density of the hatching is a function of the thickness of the layers yet to be removed.
According to a further aspect, the invention provides a method of excavating a surface layer of soil by using a excavator comprising a grab with two bucket halves having cutting edges, comprising the steps of:
a) in a first excavating position the grab is held controlled in a first orientation as seen in projection on a horizontal plane and positively lowered into the layer of soil in an open position of the bucket halves until their cutting edges reach a first predetermined level while maintaining said first orientation,
b) while maintaining that first level and first orientation, the bucket halves are moved to a closed position during which movement their cutting edges moves towards each other through a substantially straight path so as to excavate a first rectangular portion of the layer of soil,
c) the grab is lifted and moved to a discharge position horizontally spaced from the excavating position and emptied there to make further transport of the excavated soil possible,
d) the grab is moved towards a second excavating position and held controlled in a second orientation and positively lowered into the layer of soil in an open position of the bucket halves until their cutting edges reach a second predetermined level,
e) while maintaining that level and said second orientation, the bucket halves are moved to a closed position during which movement their cutting edges move towards each other through a substantially straight path so as to excavate a second rectangular portion of the layer of soil,
f) the grab is lifted and moved to a discharge position horizontally spaced from the first and second excavating positions and emptied there to make further transport of the excavated soil possible;
whereafter steps d, e and f are repeated in a corresponding manner for excavating subsequent third, fourth, etcetera rectangular portions until the layer of soil is excavated.
Thus, the orientation and level of the grab during excavating, is fully controlled.
In a further development this method includes the steps of
before step a), matching a horizontal template of congruent rectangles on the layer to be excavated, each rectangle having a centre and keeping the grab in open position defining a rectangular grab excavating opening having a grab centre,
in said first excavating position vertically matching the centre of a selected first rectangle and the grab centre and keeping the grab opening in said first orientation during the lowering and closing of the cutting edges; and
in said second excavating position vertically matching the centre of a selected second rectangle and the grab centre and keeping the grab opening in said second orientation during the lowering and closing of the cutting edges.
In this approach, the template can be composed of rectangles that are parallel to each other and/or arranged perpendicular to each other, or otherwise, such according to a radially oriented array.